Despite the use of specific antibiotics, aggressive operative intervention, nutritional support and recently, antibodies against endotoxin (ETX) and anti-cytokine therapies in septic patients, multiple organ failure continues to be a major cause of morbidity/mortality in the surgical ICU. Thus, it is essential to determine in depth the mechanism(s) underlying the pathophysiology of sepsis so that more appropriate therapeutic interventions can be designed. Prior studies, including our own, show that neither chronic low-dose ETX, at levels typically seen in polymicrobial sepsis (cecal ligation and puncture, CLP), nor tissue injury (cecal ligation,CL) alone are sufficient to induce either the late global macrophage lymphocyte immunosuppression or mortality seen in CLP. This late global CLP induced immunosuppression typified by enhanced plasma anti-inflammatory mediator release (IL-6, IL-10, TGF-beta, PGE2); increased lymphocyte Th2 cytokine (IL-4/IL-10) release; increased macrophage IL-10; and changes at the intracellular level (Ca, ATP, NFkappaB activation). Our recent data shows that necrotic tissue, but not low-dose ETX infusion alone, also induce aspects of this type of macrophage/lymphocyte anti-inflammatory response. In light of this, our hypothesis is that pro-inflammatory mediator(s) released in response to ETX, potentiate the reaction to necrotic/injured tissue (i.e., TGF-beta, IL-10, IL-4, etc.) producing an imbalance and/or exaggerated anti-inflammatory mediator response. This induces the late macrophage/lymphocyte suppression seen in polymicrobial sepsis which contributes to the animals' inability to ward off infectious microbes. We will determine the following: 1) Does chronic low-dose ETX infusion combined with CL in mice produce a similar state of both early differential macrophage activation of pro- inflammatory mediator release and the late global immune cell suppression as seen with CLP? 2) Can an alternative source of necrotic tissue other than CL (implanted syngenic donor skeletal muscle [nSM]) in the peritoneum, combined with/without low-dose ETX infusion cause a similar global immunosuppression? 3) Is the immune cell suppression seen in nSM, CL, low-dose ETX/CL or CLP mice related to changes in STAT4/ STAT6 signal transduction/activation and does deficiency of IL-10 (IL-10-/- mice) or other pathways identified, restore the suppressed immune cell response? 4) Do agents (antagonists/agonists) directed at the pro- or anti-inflammatory mediators (e.g, IL- 10 or IL-6, TGF-beta, IL-4 or PGE2), given as post-treatment, ameliorate immune cell suppression? 5) Is the enhanced macrophage NFkappaB activation seen in CLP induced by IL-10 or is it a response to an alternate component of CLP, i.e., necrotic tissue (nSM, CL) and/or ETX, and does NFkappaB activation contribute to late immunosuppression. We believe that these studies will provide new and useful mechanistic information concerning the pathobiology of sepsis.